Interesting development on this front - on EVA's website, it says you can earn miles on UA flights effective 3/3/2012...look on
http://www.evaair.com/html/b2c/engli...leage/#Airline and scroll down to United. The earning rate is not bad at all. On united.com, you can indeed select EVA Airways Evergreen Club as the frequent flyer number for your UA reservations.
You can also redeem Evergreen Club miles on United:
http://www.evaair.com/html/b2c/engli.../Award_Ticket/ - at the very bottom of the page.
Of course, Evergreen Club miles are useless and the redemption rates are terrible.
Still no sign of things working the other way. This is a good sign though.